'use strict';
var single_element = function(collection){

  let result=[];
  let arr = collection.filter(function(item,index){
    if(index%2!=0)
    return item;
  })  
  for(let num of arr){
    if(arr.lastIndexOf(num)==arr.indexOf(num))
      result.push(num);
  }
  return result;
};
module.exports = single_element;
